Glass envelope for a light emitting device and its production, particularly an envelope for a neon discharge lamp that has an internal channel.
Light emitting devices having an envelope with an enclosed, internal channel have been disclosed. Such envelopes are commonly formed from glass, are evacuated, and are backfilled with an ionizable gas. The envelope may be formed by laminating two glass sheets, or plates, at least one sheet or plate having an enclosed channel formed in a surface. The sheets may be hermetically sealed, for example, with a sealing glass frit.
It has been common practice to form an internally channeled, laminated sheet envelope by cutting channels in a bottom glass plate. The channels may be formed by grinding, etching, sandblasting, or otherwise hollowing out a desired pattern in the plate. The top plate is then sealed, as with a sealing paste, to the bottom plate to form an enclosed channel.
This procedure is too expensive and time consuming to be practical for any but special applications. Also, the weight of the finished product ralitates against such uses as automotive lights where weight is most significant. This situation has led to a search for a more practical method of producing an internally channeled, lamp envelope.
Commonly assigned, copending application Ser. No. 08/634,485 (Allen et al.) discloses such a process and the glass envelope thereby produced. The teachings of that application are incorporated herein in their entirety. The method disclosed in the application comprises successively delivering two sheets from a source of glass. A first glass sheet is delivered to a mold assembly having the desired channel forming pattern and a peripheral surface which the glass sheet overlies. The glass sheet may be caused to conform to the mold by the force of gravity, by drawing a vacuum, or by a combination of forces. The second sheet is then delivered over the conformed, bottom sheet at a viscosity such that it hermetically seals to the raised portion of the bottom sheet, but does not sag into the channels of the mold. This provides an enclosed, internally channeled, lightweight envelope in an efficient manner.
The present invention represents an improvement in the lamp envelope just described and its method of production. A lamp with the improved envelope can more efficiently focus light onto a desired target area. This means that less light need be generated with the result that input power can be reduced. Also, lamp life is known to be shortened by increased current. Thus, by reducing input power, and consequently current, lamp life can be extended significantly. Finally, the new envelope provides more design options for gas discharge lamps, particularly automotive lamps such as tail lamps.
Broadly, the invention resides in a glass envelope for a light emitting device comprising front and back members, at least one member having a continuous channel formed in one surface, the channel including connected sections alternating in dimensions, the members being hermetically joined to enclose the channel.
The invention further resides in a light emitting device comprising a glass envelope as just described wherein the envelope contains an ionizable gas and means to generate a discharge in that gas.
The invention also embodies a method of producing an envelope for a light emitting device comprising:
(a) delivering a first sheet of molten glass and depositing it on the surface of a mold having a contour including a continuous channel formed in the surface within a peripheral portion of the surface, and having alternating, connected sections of different dimensions,
(b) forming a continuous channel in the first sheet of glass corresponding to the channel in the mold by substantially conforming the sheet of glass to the contour of the mold, and
(c) delivering a second sheet of glass and depositing this second sheet over the channel in the first sheet and in contact with the peripheral portion of that first sheet,
(d) depositing the second sheet while it is at a temperature sufficient to hermetically unite with the peripheral portion of the first sheet, but insufficient to sag into the channel of the first sheet,
thereby forming a hermetically sealed, glass envelope having an internal channel having connected sections of different dimensions.